West Nile Virus

What Is West Nile Virus (WNV)?

  • A virus commonly found in Africa, West Asia, and the Middle East.

  • Carried by mosquitoes, and can cause disease in humans, birds, horses and some other mammals.

  • The most common way to get infected is through the bite of a mosquito.

  • First found in the US in 1999 in New York City, and has spread rapidly throughout other states.

  • First found in Utah in August 2003, and Utah has seen human cases of disease almost every single year.

  • Currently, there is no WNV vaccine available for humans.

  • Transmission Cycle

    Transmission Cycle

    West Nile Virus is spread by the bite of an infected mosquito, and can infect people, horses, many types of birds, and some other animals.



    • Most people with WNV will not even know they are infected. About 70-80% of people who become infected will not develop any symptoms.

    • Twenty to thirty percent of infected people will develop flu-like symptoms including fever, headache, body aches, fatigue and possibly a rash. This is called West Nile fever, and symptoms generally last only a few days.

    • A few people (about 1 in 150 persons infected) will develop a more severe form of the disease. Symptoms of severe disease may include high fever, neck stiffness, muscle weakness, confusion or disorientation. Some people may develop seizures, go into a coma, or in rare occasions, may die. Symptoms of severe disease may last several weeks with the possibility that some neurological symptoms may become permanent.

    • Other illnesses can cause symptoms similar to West Nile Virus. The only way to know if you have WNV is to run laboratory testing that can identify the virus. If you, or someone you know, is experiencing symptoms as described above or have health concerns about WNV, please contact your healthcare provider.



    Currently, there is no WNV vaccine available for humans. Prevention is KEY!

    Preventive measures to take are:

    • To protect yourself from mosquito bites. Use mosquito repellents that contain DEET when outdoors from dusk to dawn. The more DEET a repellent contains, the longer tome it can protect you from mosquito bites. For adults and children over two months of age, use repellents containing up to 30% DEET. Concentrations higher than 50 % do not provide additional protection. You should not apply repellents containing DEET to the hands or feet of children, as these repellents may cause irritation if touched to the eyes or mouth. Whenever you use an insect repellent, especially containing DEET, be sure to read and follow the directions for use carefully and for safe and effective protection.

    • Take cover. When outdoors, wear long sleeve shirts and long pants to decrese skin exposure. This provides extra protection from mosquito bites.

    • Reduce mosquitoes around your house by getting rid of all standing water.

    • Turn over or remove any kind of containers in your yard where standing water collects. This can include potted plant trays, buckets, toys, old tires, tarps, etc.

    • Clean out birdbaths and wading pools at least once a week.

    • Clean clogged rain gutters and downspouts.

    • Repair leaky faucets and sprinklers.

    • Clean and stock garden ponds with mosquito-eating fish (available from mosquito abatement districts) or mosquito dunks (small round disks that prevent mosquito larvae from hatching, available in many garden stores or supply catalogs).

    • Make sure screen doors and window screens are in good condition, and do not have any holes or loose edges that would allow mosquitoes in.

    • Keep weeds and tall grass cut short.